The broad aim of our proposed research is to gain a deeper understanding of the mechanisms of perceptual learning (PL) in normal and compromised visual systems that could potentially benefit from effective perceptual learning paradigms. We will identify the mechanisms underlying the losses and to what extent perceptual learning can ameliorate these losses. In addition, by identifying the underlying mechanisms of PL we anticipate being able to explain the large individual differences commonly found in PL studies. Aim 1) The role of context in the generalization of perceptual learning. It is generally thought that PL does not transfer across tasks. However, we show examples using Double Training where learning does generalize. We will characterize the conditions for transfer and use advanced psychophysical methods to reveal the underlying mechanisms. In the test-pedestal method, the threshold for detecting the same test stimulus is measured in different contexts. Just by changing the context the task changes, yet the ideal observer would use the same template for each task. We hypothesize that perceptual learning in one context wil not completely transfer to the related tasks. The methods will enable us to follow the development of the template during learning and what happens when the task changes even though the ideal template remains the same. Aim 2) The generalization of perceptual learning over space. The belief that PL involves modification of early visual areas is based on earlier findings that it does not transfer across retinal locations. However, our double training method does result in transfer of learning across locations, including locations that have not received any prior training. This new perspective on PL points to a crucial role for higher brain areas that engage attention and decision-making. Our preliminary studies have revealed a piggyback effect whereby promoter stimuli enable the transfer of learning of a second feature. We hypothesize the distinction of promoter is related to eye movements and global vs. local processing. Our methods enable measuring the perceptual template and its stability, provide estimates of internal noise and evaluate the role of response bias in PL. These methods are the most powerful to date to elucidate the processes associated with PL. Aim 3) Applying perceptual learning to improve visual function in people with compromised vision. Declining visual performance with age is well documented. Not surprising is the growing interest in new methods of enhancing visual function. It is reasonable to assume that training protocols can be enhanced by PL advances. By understanding the fundamental mechanisms of perceptual learning, future perceptual learning paradigms will be all the more effective in improving the quality of life of individuals with perceptual deficits, such as the elderly and persons with amblyopia. Individual differences on PL tasks are large and we have only speculative understanding of their source. Our new methods will enable us to identify the mechanisms that most account for the individual differences to provide guides for improving training methods.